More particularly, the present invention relates to the consistency of client information recorded in such a network, and thus to consistency in processing by the network of conversational data relating to such clients.
The client devices to which such resources are accessible may for example be a fixed or mobile terminal, or a residential gateway (that may be in a home or a business gateway), or indeed a voice gateway such as a DSLAM-SIP (where DSLAM stands for digital subscriber line access multiplexer, i.e. a device that collects digital subscriber line (DSL) data transiting over some number of telephone lines).
Conventional advanced session control protocols, such as SIP (standing for session initiation protocol) make use of so-called “signaling” messages, which are messages that enable a terminal to request a connection with another terminal, or likewise messages signaling that a telephone line is busy, or signaling that a called telephone is ringing, or indeed signaling that the telephone is connected to the network and may be reached in such and such a manner.
SIP is defined by the Internet Engineering Task Force (IETF) in Document RFC 3261. That protocol enables multimedia sessions to be set up, modified, and terminated in a network making use of IP. SIP also accommodates event notification procedures and the sending of information that is outside the context of a session. It is in widespread use for instantaneous messaging service commands. Thus, in an SIP environment, there exist various types of communication such as requests to set up sessions and requests that are exchanged outside any dialog.
The invention is particularly suitable for infrastructures of the IP multimedia subsystem (IMS) type. IMS is defined by the standardizing organizations of the 3rd generation partnership project (3GPP), and by telecommunications and Internet converged services and protocols for advanced networking (TISPAN). It is a network architecture introduced by the 3GPP for mobile networks, and has subsequently been taken over by TISPAN for fixed networks. That architecture, which makes use of SIP, enables multimedia sessions to be set up dynamically and controlled between two clients and also enables resources to be reserved in the network that transports the multimedia streams. By means of that architecture, network operators can conveniently implement a management policy for delivering a predetermined quality of service (QoS), and can calculate the amounts to bill their clients. At present, IMS makes it possible to access services of the telephone, videophone, presence, and instantaneous messaging types, in which it also manages interaction.
When a user seeks to benefit from services made available by an IP network, such as those described above, the user sends signaling messages to the network that may, in particular, include various types of request.
Firstly, the user terminal must register itself with the network. When the network is not capable of making the connection between that registration and an earlier registration (e.g. after a network fault, or after the terminal has been switched off for a duration longer than a predetermined value), the registration is considered as being an initial registration. After an initial registration, the user terminal must periodically send a request to the network in order to confirm that it desires to maintain its registration.
Thus, in order to be able to register clients, IP networks such as those described above include one or more servers generally referred to as serving-call server control function (S-CSCF) servers that are suitable (amongst other things) for managing the procedure for registering devices connected to the network.
In addition, those networks include one or more interrogating-call server control function (I-CSCF) servers that, when registering a client device, interrogate a home subscriber server (HSS) in order to be able to select an S-CSCF server that possesses the characteristics that are required necessarily (and, depending on circumstances, optionally) for reaching the level of service to which the client has subscribed.
Each client device may send a request to an S-CSCF server that has been allocated thereto for subscribing to certain services for the current connection. This may be an event notification service: for example, when the user of a terminal has a voice mailbox on the network, the terminal may subscribe to notification that a message has been deposited, i.e. the user may request to be informed each time a message is recorded in that voice mailbox; likewise, the user terminal may request to be notified about its registration state; it may also subscribe to a presence-notification service enabling it to receive information published by some other user it has designated, and so on. After the initial subscription request, the terminal must periodically send a request to the network in order to renew its subscription.
The above-mentioned S-CSCF servers contribute to implementing those various services by managing the routing of signaling, firstly between each client device and the network servers that are specialized in implementing such and such a service to which the client has subscribed, and secondly to other clients managed by the same network or by a network to which it is connected.
In order to be able to route those various requests within the network, servers of the I-CSCF or of the S-CSCF type (which servers are often combined as a single server, then written I/S-CSCF) exchange information with one or more servers of the above-mentioned HSS type. Each HSS contains a client database and is thus equivalent in IP networks of a home location register (HLR) of the kind used in GSM (global system for mobiles) networks. Each HSS contains the “profile” of some number of clients of the network, which profile includes their registration state, authentication and location data, and the services to which they have subscribed.
HSSs thus perform a major role in the operation of such a network, and it is essential that the dynamic information they contain is exact in order to enable the network to operate properly. That is why provision is generally made to associate each “normal” (“primary”) HSS with a “backup” (“secondary”) HSS that is ready to replace the primary HSS in the event of it suffering a fault.
However, such an arrangement has been found by the inventors of the present invention to lead to a real danger concerning consistency in how the network processes information about clients.
Here is a simple example of how inconsistency can be caused by switching over to a backup HSS in a network that has a plurality of I-CSCF servers (or functions) and a plurality of S-CSCF servers (or functions). It should be observed that in such a network, incoming calls from the public switched telephone network (PSTN) are usually distributed fairly over the set of I-CSCF servers; these servers then interrogate the HSS in order to determine the S-CSCF server to which each incoming call should be routed.
Assume for the time being that the connection between a certain I-CSCF server (referred to as the “server C2”, that also hosts an S-CSCF server) and the primary HSS becomes faulty, such that the server C2 switches over to the backup HSS. The backup HSS is then informed by the server C2 on each occasion that a client registers subsequently with the network via the server C2. If at this time an incoming call for one of these clients newly registered on the backup HSS is entrusted to the server C2, then the call will be processed correctly since the server C2 will interrogate the backup HSS in order to determine which S-CSCF is in charge of the client. In contrast, if the call for the same client is entrusted to a server other than the server C2 (this server is called “server C1”, and it likewise hosts an S-CSCF server), and if that other server C1 has not lost its connection with the primary HSS, then when the server C1 interrogates the primary HSS it will reach the erroneous conclusion that the client concerned is not registered, so the call will be routed to the client's voice mailbox instead of being transmitted directly to the client.
As explained in detail above, that problem that affects CSCF servers also affects so-called application servers (AS) such as voice messaging servers, presence servers, and telephony servers, since these ASs need to consult an HSS when depositing or recovering service data.
Unfortunately, in prior art IP networks, the above-mentioned inconsistencies do not disappear until a global restart of the network, since the problems raised by switching over to a backup HSS are not taken into account.